Chords & Harmony

Half-Diminished Seventh Chord

Definition

A half-diminished seventh chord is a diminished triad plus a minor seventh, such as B–D–F–A (Bø7 or Bm7♭5). It sits on degree 7 of a major key and is the ii chord of a minor-key ii–V–i.

A half-diminished seventh chord is a diminished triad with a minor seventh added above the root. On B it is B–D–F–A, written Bø7 or Bm7♭5. Counting half steps from the bottom, it is 3 + 3 + 4. It sounds darker and more unsettled than a minor seventh chord, but softer than the fully diminished seventh chord, and it usually leads toward a dominant.

Why "half" diminished?

Its triad is diminished, but its seventh is not: the seventh is minor, 10 half steps above the root. In a fully diminished seventh chord the seventh is diminished as well, 9 half steps: B–D–F–A♭. "Half" points to that one difference at the top.

The symbol m7♭5

Jazz charts often write it as a minor seventh chord with a lowered fifth, Bm7♭5, which describes it exactly: take Bm7 (B–D–F♯–A) and lower the F♯ to F.

Treble staff in 4/4 with two whole-note chords: B4 D5 F-sharp5 A5 labeled Bm7, and B4 D5 F-natural5 A5 labeled Bm7-flat-5. — Bm7 (B–D–F♯–A) and Bm7♭5, the half-diminished seventh (B–D–F–A). Lowering the fifth by a half step turns one into the other.

Where you find it

In a major key it is the seventh chord on degree 7: Bø7 in C major (viiø7). It works like a dominant chord, since it shares three notes with G7 (B, D and F).
In a minor key it is the seventh chord on degree 2: Bø7 in A minor (iiø7). Here it is a predominant chord that leads to V.

That second use is the heart of the minor-key ii–V–I progression: Bø7 – E7 – Am. Each chord moves to the next by small steps, and the D in Bø7 holds over to become the seventh of E7 before it falls to C.

Grand staff in 4/4, three bars of whole notes. Right hand: D4 F4 A4; D4 E4 G-sharp4; C4 E4 A4. Left hand: B2, E3, A2. Chord symbols Bm7-flat-5, E7, Am; Roman numerals ii half-diminished 7, V7, i. — Bø7 – E7 – Am. D holds from the first chord into the second, then falls to C; F steps to E and A to G♯, which rises back to A.

Bø7 on the keyboard: B, D, F and A, all white keys.

A famous example

The opening chord of Wagner's opera Tristan und Isolde, spelled F–B–D♯–G♯, sounds like a half-diminished seventh chord, although its spelling and its resolution are unusual. It is often called the "Tristan chord", and theorists have long debated how best to analyze it.

Practice with The half-diminished 7th, and train your ear with Hear the Seventh: Half-Diminished or Fully Diminished?

Common questions

What is the difference between a half-diminished and a diminished seventh chord?

Only the seventh. A half-diminished chord has a minor seventh (Bø7: B–D–F–A); a fully diminished chord has a diminished seventh, a half step lower (B°7: B–D–F–A♭).

Is m7♭5 the same as half-diminished?

Yes. Bm7♭5 and Bø7 are two names for the same chord, B–D–F–A.